Saturday, July 04, 2015

Quick Look At Today

More serious challenges for all forecasters - humans and models - on tap today. The 06 UTC run of the WRF model at Atmo forecast the MCS activity in southeast corner of state. However, the WRF-NAM moved the precipitation northward too fast, while the GFS version moved it too fast also, and to the northwest over eastern Pima County. This is illustrated above (WRF-NAM) and below (WRF-GFS) by the WRF forecasts of accumulated rainfall through 7:00 am MST this morning.

Cloud cover and outflows appear to be real Catch-22s for today. Above is visible satellite image for 7:00 am, while below is IR image for same time. Arizona is covered by heavy clouds, but the clouds extend far to the south because of several MCSs over western Mexico. The 5.4 km grid forecasts from the WRF did not forecast these more southern MCSs and their forecasts move away the clouds much too quickly today. So, outflow cooling and limited solar radiation will hold down CAPE during much of the day.

The morning sounding from TWC continues to be a mixed bag. The skewT plot of the 12 UTC data (above, from SPC) indicates only a sliver of CAPE, warm mid-level temperatures, L/V winds below 400 mb, and southerly winds at anvil levels. Most of this is negative for significant storm developments at lower elevations later today.

I took a look at the latest run of the NWS HRRR (High-Resolution Rapid Refresh) model to see what that model might be forecasting.The forecasts look fairly reasonable through the day. The forecast of composite radar echoes below is valid at 11:00 am MST this morning. The forecast area of light sprinkles and a few showers over southeast Arizona and the metro area looks reasonable, as all the MCS debris moves northward and a bit westward. For the afternoon hours, the HRRR forecasts little activity as the negative impacts of the thermodynamic structure, wind fields and MCS debris dominate.

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